Multiple printer module electrophotographic printing device

ABSTRACT

A multiple print engine system includes a plurality of print engine modules (10) that are arranged in a parallel configuration. Each of the print engine modules (PEMs) is a dedicated print engine having an associated photoconductor drum (44) and a transfer drum (42). Paper is pulled from an associated paper bin (78) or (80) and passed through the transfer nip (46) between the two drums (44) and (42). The printed copy, either made by a monochrome process or a multipass color process, is then passed through a fuser (74) to a print buffer (16) which has an associated print buffer path (104). The paper is maintained in the print buffer until it is selected by the output combiner (20). The output combiner (20) extracts the paper from the print buffer (16) at a faster rate than it was processed by the associated one of the print engines (10). The images are distributed to the various print engines by an image distributor (30) which determines which image is associated with which engine. A print manager (32) determines which of the copies in the print buffers (16) are output to the output combiner (20) and, subsequently, to an output bin.

TECHNICAL FIELD OF THE INVENTION

The present invention pertains in general to color electrophotographicprinters and, more particularly, to a plurality of print enginesarranged in parallel to process print jobs in a parallel manner.

BACKGROUND OF THE INVENTION

Electrophotographic print engines have been utilized with both printersand copiers. In a printer, the print engine is typically interfaced witha computer to select and organize fonts or bit map the images. In acopier application, the print engine is interfaced with an input devicethat scans the image onto the photoconductor drum of the print engine.However, a CCD device could also be utilized in this application in theform of a CCD scanner. In either of the applications, a conventionalprint engine for a monochrome process would typically feed a singlesheet of paper and pass it by the photoconductor drum for an imagetransfer process and then pass it to a fuser. Thereafter, the completedsheet will be output. Multiple copy print jobs will sequentially feedthe paper in a serial manner. The speed of the printer is a function ofthe speed at which the image can be created, the speed at which theimage can be transferred to the paper and the speed of the fuser. Asincreased output is required, the speed of each of these elements mustbe increased.

In a monochrome process, only one transfer operation is required.However, in a multipass color process, multiple images must besuperimposed on one another on the sheet of paper in a direct transfersystem, thus requiring multiple passes of the paper or image carrierthrough the print engine. In a double transfer system, the image isdisposed on an intermediate drum and then the composite imagetransferred to the paper or image carrier. In a multiple print job on adirect transfer system, this requires each sheet of paper to be printedin a serial manner by passing it through the print engine. For eitherthe monochrome process or the color process, a conventional serial feedprint engine has the output thereof defined by the speed of the inputdevice and the speed of the print engine itself.

One technique that has been utilized to increase throughput is a tandemprint engine. In a tandem print engine, multiple colors can be disposedon the sheet of paper or the image carrier at different stations thatare disposed in serial configuration. In this manner, the speed is thesame for one, two, three or four color printing.

SUMMARY OF THE INVENTION

The present invention disclosed and claimed herein comprises a multipleprint engine. The multiple print engine includes a plurality ofelectrophotographic print engine modules, each of the modules operableto receive an image file and print an image on an image carrier that isassociated with the image file. A plurality of print buffers areprovided, each associated with the output of at least one of the printengine modules. The print buffers are operable to receive the output ofthe associated one of the print engine modules as a completed print job.An output collator is provided for selectively feeding the output ofeach of the plurality of buffers.

In another aspect of the present invention, an image distributor isprovided for distributing an input sequence of images to each of theprint engine modules in a predetermined order. A print manager isprovided for determining the sequence in which the output of the printbuffers are retrieved. In one embodiment, the output sequence is thesame as the input sequence to the image distributor.

In a further aspect of the invention, a print completion indicator isprovided for indicating when each of the print engine modules hascompleted a print job and is ready to receive another image file. Afailure indicator is provided for indicating when a print engine modulehas not completed a print job and does not generate the print completeindication. In this event, the image file is stored in a buffer and theimage distributor can thereafter route this to another print enginemodule for completion of the print job.

In yet another aspect of the present invention, each of the print enginemodules is operable to complete a print job at a first print speed. Thecollator is operable to retrieve each of the print jobs from the printbuffers and route them to a single output at a second speed. The secondspeed is faster than the first speed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying Drawings in which:

FIG. 1 illustrates an overall block diagram of the multiple module printengine;

FIG. 2 illustrates a cutaway side view of a three module multiple printengine;

FIG. 3 illustrates a block diagram of the printer management system;

FIG. 4 illustrates a block diagram of the print engine manager;

FIG. 5 illustrates a block diagram of the image flow from the imagedistributed to the marking engine;

FIG. 6 illustrates a timing diagram for throughput between a multipleprint engine printer and a tandem printer;

FIG. 7 illustrates a diagram of the paper feed device on the outputillustrating the print buffer;

FIG. 8 illustrates a detail of the duplex paper feed operation;

FIG. 9 illustrates a flowchart for the overall process flow;

FIG. 10 illustrates a flowchart for the process queue;

FIG. 11 illustrates a flowchart for the page separator;

FIG. 12 illustrates a flowchart for the paper path manager; and

FIG. 13 illustrates a flowchart for the print manager operation.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is illustrated a block diagram of theoverall print engine system. A plurality of print engines 10 areprovided, each print engine 10 operable to receive an image inelectronic form, convert this image to a latent image disposed on aphotoconductor drum (not shown), develop it and then transfer it to animage carrier such as paper, for transfer to a fuser and then outputtherefrom. This will be described in more detail hereinbelow. Theseprint engines 10 can operate as either a black and white engine or acolor engine requiring multiple passes. Each of the print engines 10 isinterfaced with a dedicated paper supply bin 12 which is operable tofeed paper to the associated print engine 10 through a feed rollerdevice 14. At the output, each of the print engines 10 is operable tofeed the paper and the image disposed thereon to an associated printbuffer 16 via a paper feed device 18. Thereafter, the print buffers canbe controlled to selectively output the contents thereof through anoutput combiner 20 via a feed roller 22. As will be describedhereinbelow, the speed of the feed rollers 22 can be varied relative tothe speed of the print rollers 18. The output combiner 20 operates at amuch higher speed than the print rollers 18, as it must collect theoutputs of all of the print buffers or portions thereof. The outputcombiner 20 is operable to output the paper collected from each of theprint buffers 16 to an output bin 23 via a feed device 24.

The image is provided through an image input device 28 which, for arelated printer application, can be a PC, and for a copier applicationcan be a CCD scanner. The image input device 28 is then operable toprovide an electrically coded image signal to an image distributor 30,which image can then be stored in an image buffer 32. The imagedistributor 30 is operable to select and output the image of each pageto select ones of the print engines 10 in accordance with a parsingalgorithm.

The printing operation is controlled by a print manager 34, which isoperable to control each of the print buffers 16. Each of the printbuffers 16 is operable to store a sheet of paper and then selectively"eject" that sheet of paper upon receiving a command from the printmanager 34. The print manager 34 also controls the output combiner 20 todetermine the speed at which it pulls paper from the print buffer 16.The overall system is controlled by a system controller 36.

In operation, a print job is input to the system through the inputdevice 28. This is a sequential operation. At this time, the imagedistributor 30 can determine which of the print engines 10 will printwhich copy. Since each page can have a different content thereto, theprocessing time for each page will vary, dependent upon the amount oftime required to create the latent image on the photoconductor drum. Theimage distributor 30 determines this and then routes the page to a givenone of the print engines 10. The print manager 32 operates inconjunction with the image distributor 30 such that, when the image issuccessfully transferred to the paper and is stored in the print buffer16, the correct order in which the pages have been entered can bereconstructed, as will be described in more detail hereinbelow. In orderto do this, however, the speed at which the paper is extracted from theprint buffer 16 is much faster than the speed at which the paper isinput to the print buffer 16. Further, since each sheet of paper maytake a different amount of time to process and dispose the sheet in theprint buffer 16, the speeds of the driving devices 22 may be varied evenrelative to each other.

Referring now to FIG. 2, there is illustrated a cutaway side view of athree print engine module parallel printer which includes three printengines 36, 38 and 40, all stacked one on top of the other. Each of theengines 36, 38, 40 is a multi-pass engine and includes a transfer drum42 and a photoconductor drum 44. The photoconductor drum 44 rotates in acounterclockwise direction and is pressed against the transfer drum 42to form a nip 46 therebetween. The photoconductor drum 44 is operable tohave the surface thereof charged with a corona 48 and then an imagingdevice 50 is provided for generating a latent image on the chargedsurface of the photoconductor drum 44. The undeveloped latent image isthen passed by four developing stations, three color developingstations, 52, 54 and 56 for the colors yellow, magenta and cyan, and ablack and white developing station 58. The color developing stations 52,54 and 56 each have a respective toner cartridge 60, 62 and 64associated therewith. The black and white developing station 58 has ablack and white toner cartridge 66 associated therewith. Although notdescribed hereinbelow, each of the developing stations 52, 54, 56 and 58and toner cartridges 60, 62, 64 and 66 can be removed as individualmodules for maintenance thereof.

During the print operation, the photoconductor drum 44 is rotated andthe surface thereof charged by the corona 48. An undeveloped latentimage is then formed on the surface of the photoconductor drum 44 andthen passed under the developing stations 52, 54, 56 and 58. In amulti-pass operation, the latent image is generated and only one colorat a time utilized in the developing process for the latent image. Thislatent image is then passed through the nip 46 and transferred to animage carrier, such as paper, which is disposed on the surface of thetransfer drum 42. Thereafter, the surface of the drum 44 is passed undera cleaning station 68, which is operable to remove any excess tonerparticles which were not passed over to the transfer drum 42 during thetransfer operation and also discharges the surface of the drum 44. Thesystem then begins generation of another latent image, either for adifferent color on the same sheet of paper or the first color on adifferent sheet of paper.

In the color operation, multiple passes must be made such that the imagecarrier, i.e., paper, remains on the surface of the transfer drum 42 forthe multiple passes. In the first pass, the first latent image istransferred to the surface of the photoconductor image carrier and drum44, developed and then the development is transferred to the imagecarrier maintained on the transfer drum 42. The development of the nextlatent image of the next color is superimposed on the development of thefirst latent image, it being noted that the registration is important.This registration is provided by the mechanical alignment of the variousdrums, drive mechanisms, etc. Thereafter, the third color latent imageis developed and disposed on the image carrier followed by the fourthcolor latent image.

After the last color latent image is development and disposed on theimage carrier in the color process, a picker mechanism 72 comes down onthe surface of the transfer drum 42 in order to lift up the edge of theimage carrier or paper. This is then fed to a fuser mechanism 74.

The image carrier is typically comprised of a predetermined weightpaper. The transfer drum 42 utilizes electrostatic gripping for thepurpose of adhering the paper to the surface of the transfer drum 42 formultiple passes. This therefore utilizes some type of charging mechanismfor charging the surface of the drum 42 at an attachment point 76 wherethe paper is fed onto the surface of the transfer drum 42. The transferdrum 42 is, in the preferred embodiment, manufactured from a controlledresistivity type material that is disposed over an aluminum supportlayer which is a hollow cylindrical member. A voltage supply is providedthat provides a uniform application of voltage from the voltage supplyto the underside of a resilient layer that is disposed over the surfaceof the aluminum support member. This resilient layer is fabricated froma carbon filled elastomer or material such as butadaiene acrylonitorile,which has a thickness of approximately 3 mm. Overlying this resilientlayer is a controlled resistivity layer which is composed of a thindielectric layer of material at a thickness of between 50 and 100microns. This controlled resistivity layer has a non-linear relationshipbetween the discharge (or relaxation) point and the applied voltage suchthat, as the voltage increases, the discharge time changes as a functionthereof. The paper is then disposed over the surface of the drum. Theconstruction of this drum is described in U.S. Pat. No. 5,459,560,issued Oct. 17, 1995, and entitled, "Buried Electrode Drum for anElectrophotographic Print Engine with a Controlled Resistivity Layer"(Atty. Dkt. No. TRSY-21,888), which is a continuation-in-part of U.S.patent application Ser. No. 07/954,786, filed Sep. 30, 1992, andentitled, "Buried Electrode Drum for an Electrophotographic PrintEngine" (Atty. Dkt. No. TRSY-21,072), which U.S. patent application Ser.No. 07/954,786, is incorporated herein by reference.

The paper is retrieved from one of two paper supply bins 78 or 80. Thepaper supply bin 78 contains one type of paper, typically 81/2"×11"paper, and the paper bin 80 contains another type of paper, typically81/2"×14" paper. The paper bin 78 has the paper stored therein selectedby a first gripping roller 83, which is then fed along a paper path 80into a nip 82 between two rollers and then to a nip 84 between tworollers. This is then fed to a paper path 86 to feed into a nip 88between two rollers. The paper in the nip 88 is then fed into a nipformed between two precurl rollers 90 and 92, which have differentdurometers to cause the paper to have a curl bias applied thereto in thedirection of the curvature of rotation of the transfer drum 42. Theoperation of the pre-curl rollers is described in detail in U.S. Pat.No. 5,398,107, filed Mar. 14, 1995, and entitled, "Apparatus for Biasingthe Curvature of an Image Carrier on a Transfer Drum" (Atty. Dkt. No.TRSY-22,574). The paper from the bin 80 is extracted by a grippingroller 89 and pushed along a paper path 91 to the nip 88 and therefromto the pre-curl rollers 90 and 92.

The paper is fed from the nip between the two pre-curl rollers 90 and 92at the attachment point 76. At the attachment point 76, an attachmentelectrode roller 94 is provided which is operable to operate on a cammechanism (not shown) to urge the roller 94 against the surface of thedrum 42 to form the attachment nip 76. This is done during the initialattachment of the paper to the drum 42. Typically, this attachmentelectrode roller 94 is connected to ground. The surface of the drum 42is charged to a positive voltage of between 800-1,000 volts. The voltageis disposed on the surface of the drum 42 by a positive electrode roller96 that contacts the surface of the drum 42 at a point proximate to thephotoconductor drum 44. Since the electrode 94 is grounded, the voltagewill decrease along the surface thereof until a lower voltage is presentat the attachment point 76. When the paper reaches the transfer nip 46,the portion of the surface of the photoconductor drum 44 in the nip 46has a potential thereof reduced to ground such that the chargedparticles will be attracted from the surface of the photoconductor drum44 to the surface of the paper on the drum 42.

For a multiple pass operation, the attachment electrode 94 will bepulled outward from the drum 42 and the paper allowed to remain on thedrum 42 and go through the transfer nip 46 for another pass. When thefinal pass has been achieved at the transfer nip 46, the picker 72 isswung down onto the surface of the drum 42 to direct the paper on thesurface of the drum 42 to the fuser 74. A discharge electrode 98 is thenswung down into contact with the drum 42 to provide a dischargeoperation before the surface of the drum enters the nip 76 for the nextpaper attachment process.

When the paper is fed into the fuser 74, it is passed into a nip betweentwo rollers 100 and 102, both of which have different durometers.Typically, there is one roller that is formed from a metallic materialand one roller that is formed of a soft material. The rollers areoriented with the roller 100 having the smaller durometer, such that areverse bias curl will be applied to the paper that is the oppositedirection of the curvature of the drum 42. This will remove thecurvature added to the paper. One of the rollers 100 is heated such thatthe transferred image is "fused". The paper is then fed into a paperpath 104 by a pair of rollers 106, which, as will be describedhereinbelow, is a "buffered" paper region. A duplex paper path 108 isalso provided, which will be described hereinbelow.

Thus far, the operation of the print engine has been described as aconventional electrophotographic print engine. However, the use of thebuffer path 104 is different, as will be described hereinbelow. Each ofthe roller pairs 106 operates at the speed of the associated one of theprint engines 36, 38 or 40 to dispose the paper in the associated one ofthe buffered paper paths 104. Thereafter, the paper is input to theoutput combiner 20. The paper path 104, has a plurality of rollers (notshown) associated therewith for each of the print engines 36, 38 and 40,as will be described hereinbelow.

Each of the paper buffer paths 104 is operable to feed the paper up toone of three output paper path points 110, 112 and 114, associated witheither of the print engines 36, 38 and 40, respectively. Thereafter, theprint manager 32 controls the rollers associated with each of the printbuffer paths 104 to selectively move the paper into a nip 116 between aroller pair 118. When this occurs, the paper is led at a much higherspeed than the speed with which it was initially placed into the bufferpath 104. Therefore, the rollers pair 106 that inputs the paper to theprint buffer path 104 operates at the speed of the print engine, whereasthe rollers internal to the buffer paper path 104 and the output roller116 of the output roller pair 118 operate at a variable speed, dependingupon the speed at which the paper must be extracted. This can be atleast three times as fast as the fastest print speed, it being notedthat the speed of each of the engines is a function of the time it takesto create and transfer the latent images and the time that is requiredto go through the fuser. In certain situations, with relatively simpleimages, this can be relatively fast, whereas complicated images may takemore time. In any event, the printer buffer allows the image distributorto distribute an image to any one of the three print engines, 36, 38 and40, but change the sequence of the output selection.

Referring now to FIG. 3, there is illustrated a block diagram of theprint manager system (PMS) for controlling the overall operation of eachof the print engines 36, 38 and 40. The overall page reading and errormanagement tasks are controlled by a control task center, which isreferred to as a "PMS Control Task" block 120. The PMS Control Taskblock 120 is interfaced with a user interface block 122 that allows auser to input data to the PMS Control Task block 120 in the form ofcontrols, such as the number of copies to be printed, all sortoperations, etc. Further, data can be downloaded from the user interface122. When information is input to the system, it is input from an I/Omanager 124 which is operable to receive the basic image information.The image information is then queued up in accordance with a job queuemanager 126 and then, when the page is already printed, process itthrough a job decomposer (page separator) block 128. Once the job hasbeen decomposed, i.e., separated into pages, the image is transferred tothe PMS task block 120. In this operation, the block 120 interfaces witha page queue manager block 130, which page queue manager determines thejob parsing algorithm, which defines the PM manager to which the page isto be routed. This is also controlled by a paper path manager block 132and a resource/font manager 134.

The PMS control task block 120 is operable to interface with each of theprint modules and print engines associated with the printing devicewhich is referred to as PEM manager. A plurality of PEM managers, PEMManager 0-PEM Manager n-1, are provided, and referred to by referencenumerals 136. The connection between the PEM Manager to the associatedPEM is via a high speed communication link 138. This can be any type ofcommunication link that allows data to be transferred between the twosystems. In general, each of the PEM managers can operate asynchronouslyand independently of the PMS Task Control block 120, it being noted thatthe PMS Task Control block 120 and all of the associated functionsprovided thereby are provided in a typical personal computer. It is onlynecessary that information be transferred to select ones of the PEMmanagers 136. Such communication links are conventional. The high speedlink is a bi-directional parallel port utilizing conventional personalcomputers, an IEEE P 1284 or ECP extended capabilities port. Further,the PEM managers 136 could be configured such that they are integratedwith the overall processor of the PMS Task Control block 120 and theassociated PMS functions. This would merely require a multitaskingoperation to occur in one single computer with hardware connections todrive various logic circuitry on the print engine modules themselves.

Referring now to FIG. 4, there is illustrated a block diagram of the PEMoperation. A printer communication manager 140 is provided which isoperable to interface with a printer status manager 142 that determinesthe applications, such as when the printer is available, if the printeris busy, if there is a printer error, if the printer is ready to ejectthe page, or whatever the general component status is. The data ispassed along a data path 144 which is operable to merge with the controltask to a line 146 from the printer status manager 142 to output thetask, which can be control of the printer, transfer of data, etc.Further, signals can be received back from the various systemsindicating error states, eject status, etc. Further, the printercommunication manager 140 is in contact with a fuser temperature/powermanager 148, which provides overall control of the system, this beingconventional. In general, the printer communication manager 140 isoperable to receive from the print engine data and commands indicatingwhat sheet of paper should be printed and whether a sheet of paper,after printing, is to be ejected from the print buffer 16. Further, thisstatus can be relayed back to the print manager system.

Each of the print engine modules (PEM) is designed as an optimal lowcost, high reliability and high print quality unit which, when assembledin multiples of the system configuration, exceeds the performance andreliability of a single print engine system at comparable overall pageprinting speeds including RIP times. Each of the modules includes anassociated RIP and memory. Since the print engine module operates at amuch lower speed than the overall output of the printing system, thecost and the reliability is much improved as that for a single highspeed system. The print management system provides the ability tobreakdown incoming jobs into its individual pages and to separateprinting data (data flow) from media page (paper flow) operations andmanagement within the system. Although the PMS allocates printing datato the respective PEM, the decision of which PEM, the timing of therelease to printing and the media output flow through theserver/collator is controlled by the PMS. When the image is routed tothe PEM, it is input to the Raster Image Processor (RIP), associatedwith that PEM. This is a dedicated RIP which, from an overall systemstandpoint, results in parallel RIPs. As such, the system does notrequire one high speed RIP that would increase complexity; rather,multiple modified RIPs are provided which allow the overall system speedto be increased without surpassing the performance limitation of thecurrent RIP technology levels that exist to support high speed pageprinting. This is particularly true for Page Description LanguageProcessing. The PostScript Page Description Language is not suited forparallel processing to decrease the RIP time and current printerdesigns. The PostScript PDL which is not well suited for parallelprocessing is essentially paralleled by dividing a single job intoseveral pages.

During operation, the PMS will provide the overall control of systemaccess, utilization of the various modules, the job assignments tovarious modules and the output assembly of printing jobs that aredispatched to the system. Further, the PMS will act as a resource (fontand bit map image, etc.) server for the system to determine what fontsare to be used and how the images are to be distributed. It alsomaintains knowledge of the PMS and PEM and job status to assurecontinuity from receipt, dispatch, interruption, recovery and completionof job assignments. If a job is too complex and non-conforming to breakup into simple pages, it simply sends the entire job to a single PEM.The overall system can also send notices of job completion to the usersand accumulate job status for allocating jobs to those users.Additionally, errors can be noted in the printing operation such that,for example, if one of the modules jams during a print operation, thisprint job can be returned to the PMS and the job sent to another printerfor handling thereof.

By way of example, the following table will provide a comparison betweenthe multiple printer system (MPS) and a tandem printing system. Table 1illustrates the time in seconds for the RIP of each of the modules inthe MPS to process a page of a ten page PostScript document for both thetandem system and the MPS system. It is noted that the tandem systemprovides a much faster per page time (2X).

                  TABLE 1                                                         ______________________________________                                        TOTAL RIP TIME                                                                Total RIP Time                                                                Page           Tandem   MPS                                                   ______________________________________                                        1              5 sec    10 sec                                                2              7 sec    14 sec                                                3              6 sec    12 sec                                                4              8 sec    16 sec                                                5              8 sec    16 sec                                                6              5 sec    10 sec                                                7              5 sec    10 sec                                                8              4 sec     8 sec                                                9              4 sec     8 sec                                                10             4 sec     8 sec                                                Total          56 sec   112 sec                                               ______________________________________                                    

The tandem technology printer, as described above, provides a stationfor each color, such that once the multiple colors have been processed,the time for a given page essentially equals that of a single page. Bycomparison, each of the PEMs in the MPS processes a page for a muchlonger time. It should be noted that each of the pages in the PostScriptdocument is different, resulting in different times.

From Table 1, it can be seen that it take approximately 56 seconds tocomplete the job on the tandem printer. The RIP processing time is thelimiting factor in this case since most of the pages take more than 4seconds to RIP while the page print speed, which is overlapped withprocessing, is approximately 3 seconds. By comparison, if the MPS systemoperated in a serial manner, it would take 112 seconds. However, the MPSdoes not operate in a serial manner; rather it operates in a parallelmanner.

Referring now to FIG. 5, there is illustrated a block diagram of theoverall operation of transferring information from the image distributor30 to the PEM. In general, the PEM contains a RIP 147, an image buffer149 and a marking engine 151. The process flow of FIG. 5 is directedtoward a single PEM. Initially, the image distributor 30 is operable toreceive the image information and create an object representationthereof. This object representation is what is transferred to the PEM. Asingle one of the high-speed transmission paths 138 is illustrated forcarrying the object representation to the PEM. At the PEM, the objectrepresentation is received by the RIP 147. The RIP 147 is then operableto convert the object representation to a pixel representation. Thispixel output will represent the image and this image is stored in animage buffer 149. The overall print operation of the print engine moduleis performed by a "marking engine" 151, which marking engine 151 isgenerally comprised of the mechanical components necessary to form alatent image, develop that latent image and then transfer it to an imagecarrier.

When forming the object representation of the image, the imagedistributor 30 determines what information is necessary to include inthe object representation. The particular print file type for thedocument, i.e., PostScript, PCL, etc., is encoded into the objectrepresentation, along with the necessary overhead associated with thatimage file. This overhead is the information regarding font types,particular printer control information, etc. that is necessary in orderfor the printer engine module to properly process the image file. Forexample, each printer engine module may have "resident" fonts associatedtherewith. However, there are some fonts which are referred to as "softfonts", which are downloaded as software to the printer engine moduleand maintained in volatile memory. If this type of font is required, itis necessary to load the font into the volatile memory at sometime inthe operating process. Of course, if memory is not a problem, eachprinter module could be initialized upon power up with all necessaryfonts. However, with the large number of fonts that exist in printerstoday, the typical procedure is to select the necessary fonts that arerequired for a particular page and then transmit these to the printeralong with the page information. It should be noted that this issomewhat different from processing a document as a whole with a singleprinter since this method only requires the fonts to be transmitted tothe printer upon initiation of the print job and load them in thevolatile memory. Thereafter, each page can be processed withoutrequiring the files to again be downloaded at the beginning of the page.

Referring now to FIG. 6, there is illustrated a timing diagram forcomparison between the tandem printer and the quad-print engine MPSprinter. The timing diagram is incremented in increments of 2 seconds.In the first 2 second increment, the tandem printer initiates page 1 andthe MPS printer initiates pages 1-4. In the 6 second timeslot, thetandem printer finishes page 1 and begins page 2. In the 8-10 secondtimeslot, the MPS printer finishes page 1 and begins page 5 with page 1ejected. In the 10-12 second timeslot, the tandem printer finishes page2 and begins page 3, whereas the MPS printer finishes page 3 and beginspage 6. In the 12-14 second timeslot, the MPS printer finishes page 2,begins page 7 and ejects pages 2 and 3. In the 14-16 second timeslot,the MPS printer finishes printing page 4, begins printing page 8 andejects page 4. In the 16-18 timeslot, the tandem printer finishes page 3and begins page 4. In the 20-22 timeslot, the MPS printer finishes page6 and begins page 9 and, in the 22-24 timeslot, the MPS printer finishespage 7, finishes page 8 and begins page 10. In the 26-28 secondtimeslot, the MPS finishes page 5 and ejects pages 5, 6, 7 and 8,whereas the tandem printer finishes page 4 and begins page 5. In the28-30 second timeslot, the MPS printer finishes page 9 and ejects page9. In the 30-32 second timeslot, the MPS printer finishes page 10 andejects page 10. The tandem printer continues printing until it finishespage 10 in the 54-56 second timeslot. It can be seen that the MPSprinter, operating in parallel, finishes the print job after 32 seconds,whereas the tandem printer required 56 seconds.

The distribution of the print jobs and the eject operations arecontrolled by a job parsing algorithm. This job parsing algorithmrequires that the print buffer be present such that the eject time canbe selected, and this eject time is done at a faster speed than theactual print operation paper flow for each module in the MPS printer.For example, it can be seen that page 3 in the above example, associatedwith FIG. 6, was finished in the 10-12 timeslot, whereas it was notejected until the 12-14 second timeslot. Further, it can be seen thatpage 6 was actually finished printing in the 20-22 second timeslot andpage 5 was finished printing in the 24-26 second timeslot, but page 6and page 5 were ejected during the same timeslot, the 20-26 secondtimeslot. Therefore, the job will be output in the same sequence that itwas initiated. The difference between the tandem operation and the MPSprinter operation is due to the fact that the tandem unit would performthe job in a page-by-page sequence, overlapping RIP operations withprinting after the first page was printing. On the MPS printer, the jobis split up by the PMS as it is received, sending page information tothe PEMs in a predetermined order.

In a monocolor example, a single color page may be printed in, forexample, a job batch of 100 copies. If the RIP time for the page is 10seconds for the tandem unit and 20 seconds for the MPS printer, thetandem unit will print the monocolor pages at 20 pages per minute. TheMPS PEMs each print monocolor at 16 pages per minute. The time tocomplete the job in the tandem unit is equal to the RIP time for eachpage, incurred just once, plus the time to print the 100 pages. Thetotal elapsed job time is 10 seconds RIP time plus 100 pages at the 20pages per minute rate of speed of the tandem unit, i.e., 5 minutes and10 seconds. With the MPS printer, all four PEMs will operate inparallel. The time to complete the job is equal to the PEM RIP time,incurred just once in parallel, plus the time to print the 100 pages--25pages per PEM. The total elapsed time is 20 seconds RIP time plus 25pages at the 16 pages per minute monocolor print speed of the PEMs--1minute and 35 seconds. The job is completed about three times tasterthan the tandem engine.

If a full color copy is to be printed on a job batch of 100 copies for asingle color page, the tandem printer job time is exactly the same asthe monocolor example, which is 5 minutes and 10 seconds. However, theMPS operates to utilize all four PEMs in parallel. The time to completethe job with the MPS printer is equal to the PEM RIP time incurred justonce in parallel, plus the time to print the 100 pages--25 pages perPEM. However, the print speed for four color pages on each PEM is 4pages per minute. Therefore, the total elapsed job time is 20 secondsRIP time plus 25 pages at the 4 pages per minute four color print speedof the PEMs--6 minutes and 27 seconds. The job is completed about 20%faster on the tandem engine.

In general, the MPS provides a significant improvement over the tandemsystem for typical jobs that include both text and graphics. Since mostjobs that include the text and graphics result in a page RIP time thatis usually longer than the rated printing time, the MPS system would beapproximately two times faster than the high performance tandem unit forboth monocolor and full color jobs. If a page of the jobs were simplecached text and the limiting factor was the printing speed, the MPSsystem would be about three times faster for monocolor and a bit slowerfor full color than a 20 page per minute tandem printer. However, itshould be noted that no RIP implemented with present technology can keepup with the 20 per minute page full color engine. If more MPSperformance is needed, speed or capacity could be achieved by increasingthe number of PEMs in its configuration.

Referring now to FIG. 7, there is illustrated a block diagram of thepaper feed path. Only two of the PEMs are illustrated, the first PEM 36and the second PEM 38. The paper path 104 in the buffer for the firstPEM 36 has three sets of rollers, 150, 152 and 154, associatedtherewith, the set of rollers 154 being the exit set of rollers for theprint buffer for the PEM 36. Each of the roller sets 150, 152 and 154,is comprised of a driven roller and an idler roller to form a niptherebetween. The distance between the nip in the roller 154 and the nipbetween the fuser rollers 100 and 102 is greater than the length L1,which represents the longest length of paper to be processed by theprint engine. As such, paper can be fed into the print buffer such thatit is held in the nip at the rollers 154 but has exited the nip betweenthe fuser rollers 100 and 102. An exit sensor switch 156 is provided atthe input to the paper path 104 at the buffer associated with the PEM 36to indicate that paper is present in the print buffer and has exited thefuser.

When paper is input to the print buffer, it is moved at the speed of thePEM 36. Therefore, the speed at which the fuser rollers 100 and 102passes the paper therefrom defines the speed at which the print buffercan be loaded. Therefore, the rollers 150, 152 and 154 must operate atthat speed during the load operation. Upon merging of the documents intothe merge roller 118 and the nip therebetween, the system operates at ahigher speed. During this operation, the rollers 154 must operate at thehigher speed which, for a three PEM MPS is three times the speed of asingle PEM. The rollers 154 must operate at the higher speed, andtherefore, the driven roller is driven by a two-speed motor. The rollers150 and 152 can operate as one speed motors with overrun clutches toallow the paper to be pulled therefrom at the higher speed. Further,they could utilize two-speed motors on the driven roller.

The paper path 104 associated with the PEM 38 is illustrated as havingfour sets of rollers associated therewith, rollers 160, rollers 162,rollers 164 and rollers 166, rollers 166 comprising the exit rollers ofthe print buffer for the PEM 38. An exit paper sensor 168 is provided atthe output of the fuser rollers 100 and 102 for the PEM 38. As was thecase with the buffer for the PEM 36, the rollers 166 operate on twospeeds. The distance between the exit rollers 166 and the nip at thefuser rollers 100 and 102 might be greater than the length of thelongest sheet of paper, this being represented as a length L2. Ofcourse, the configuration illustrated in FIG. 6 shows a much longerpaper path 104 for PEM 38 as compared to PEM 36. However, the mergepoint could be distributed along the length of the MPS and does notnecessarily have to be a single point on the exit rollers 118. Therecould be multiple merge points. Further, the PEMs do not have to bestacked and there could be a much more complex merge mechanism orcombiner 20.

Referring now to FIG. 8, there is illustrated a detail of the duplexpath operation. In a normal operation, the paper is extracted from thebin via a paper path 172 and fed into the nip between the precurlrollers 90 and 92 and then into the attachment 76 and then onto thetransfer drum 42 for receiving the transferred image, after which it ispassed to the fuser between rollers 100 and 102 and then passed outwardto the print buffer paper path 104. The rollers 88 are operable to pullthe paper up into the print path 104 with a paper deflector mechanism174 being disposed in a non-interfering position such that paper can beremoved from the fuser rollers 100 and 102 and placed into the printbuffer paper path 104. In a duplex operation, the rollers in the printbuffer paper path 104, rollers 150 and 152 for the PEM 36, are thenoperable to reverse direction. In this mode, the paper deflectionmechanism 174 is disposed downward to force the paper along the duplexpaper path 108. Two sets of rollers, rollers 176 and rollers 178,control the flow of the paper along this path to direct it to the nipbetween the precurl rollers 90 and 92. Since the trailing edge of thepaper in the first path now becomes the leading edge, the paper iseffectively turned over such that an image can be disposed on theopposite side thereof. Thereafter, the operation takes place in a normalmanner and the paper is then placed in the print buffer paper path 104.

Referring now to FIG. 9, there is illustrated a flowchart depicting theoperation of the overall process flow. The program is initiated at ablock 180 and then proceeds to a function block 182 to receive the job.Initially, the job is converted to an appropriate object file in thecase where a printer application is present. For example, the objectfile could be a PCL file. With respect to a copier application, thiswould typically be a pixel file, since the pixels are directly read froma CCD scanner and can therefore be directly input to the printer. Theprogram then flows to a node 184 which has three parallel pathstherefrom. The first path flows to a decision block 186 to determine ifthere is a job queuing period. If so, the program will flow to afunction block 188 to save the job on disk for the purpose of providinga backup thereto. The program then flows to the node 184. If a job isnot queuing, the program will also flow from a decision block 186 tonode 184. A second path from the node 184 flows to a function block 190to perform the fuser tasking operations which are basically directedtowards power management of the fusers, which operation will not bedescribed herein.

The program flows from the node 184 along a main path to a decisionblock 192 to determine if any pages are left to be processed. If so, theprogram will flow along the "Y" path to a function block 194 to separatethe pages and then add resources, i.e., start up another print engine.The program will then flow to a decision block 196 to determine if pagebuffering is on. If page buffering is on, the program will flow along a"Y" path to a function block 198 to save the page and the associatedresources, the resources being the various parameter information thatfollows the page through the processing such as the font informationassociated with the page, etc.. The program will then flow to the outputof decision block 196. The buffering process allows the page to be savedfor the purpose of printing it at a later time or for printing multiplecopies. If the page buffering is not on, the program will flow from thedecision block 196 to a function block 200 to queue the page for thenext available engine and then back to node 184.

When all pages have been queued up, the program will flow to a functionblock 202 along the "N" path from the decision block 192 to perform acleanup operation. The program will then flow to a function block 204 toperform the fuser tasks and then to a Done block 206.

Referring now to FIG. 10, there is illustrated a flowchart depicting theprocessing operation of the pages in the queue. The program is initiatedat a block 210 and then flows to a decision block 212 to determine ifthere is a page in the queue. If not, the program will flow back to theinput of decision block 212 along the "N" path thereof until a page hasbeen disposed in the queue. At this time, the program will flow alongthe "Y" path to a decision block 214 to determine if there is anavailable engine. If not, the program will flow along the "N" path backto the input of decision block 214. When an engine becomes available,the program flows along the "Y" path from decision block 214 to afunction block 216 to send a page to the print engine. In the case of aprinter, this could be a PCL file or a PostScript file, and in the caseof a scanned image in a copier application, this could be a pixel file.This is all achieved over a high speed data link. The program will thenflow to a function block 218 to inform the paper path manager that thepage has been sent. The program then flows back to the input of decisionblock 212.

Referring now to FIG. 11, there is illustrated a flowchart depicting theoperation of the page separator. The program is initiated at a block 220and then flows to a decision block 222 to determine if the page is thefirst page. If so, the program flows along the "Y" path to a functionblock 224 to determine the language of the object file that is receivedand to initialize the printer for that language. If, for example, thelanguage were PostScript, it would be important that the RIP operateunder this language. The program would then flow back to the output ofdecision block 222. If the received page was not the first page, theprogram flows along the "N" path from the output of the decision block222 to the input of a decision block 226 to determine if the header orresources were included in the page. If so, the program flows along a"Y" path to a function block 228 to save the header or resource and thento the output of decision block 226. If no header or resources areincluded, the program flows from the output of decision block 226 alongthe "N" path thereof to a decision block 230 to determine if the headeror resources are required for this page, i.e., font information, etc. Ifso, the program flows along a "Y" path to a function block 232 to loadthe header resources and then back to the output of the decision block230. If a header or resources are not required, the program flows alongthe "N" path from the output of decision block 230 to the input of adecision block 234 to determine if the end of the page has occurred. Ifnot, the program flows along the "N" path to a function block 236 tosave the current information in the queue and then back to the input ofthe decision block 234.

The function block 236 represents an operation wherein a single page canbe buffered in the event that a signal has not been received from theprint engine indicating that the page has been printed, i.e., an end ofpage signal. If the end of page signal is not received, this indicatesthat the printer has jammed or there has been some error in the printingoperation. If so, the information is still stored and it can beretransmitted to a separate engine. However, once the end of a page hasbeen received, this indicates that the page has been printed and isstored in the appropriate print buffer. The program would then flowalong the "Y" path from the decision block 234 to the input of afunction block 238 to process the copy count information and then to aDone block 240.

Referring now to FIG. 12, there is illustrated a flowchart depicting theoperation of the paper path manager. The program is initiated at a block242 and then proceeds to a decision block 244 to determine if the pagebuffer in the selected engine is full. If so, the program will flow to adecision block 246 to determine if the received page is the next page inthe sequence. If so, the program flows along the "Y" path to a functionblock 248 to send the buffered page to the collator and then to afunction block 250 to update the empty status as having an empty buffer.If the page buffer in the selected engine was full, the program wouldflow along an "N" path from the decision block 244 to a function block252 to increment the system to select the next engine in the sequenceand then back to the input of decision block 244. This would also be thecase if it were determined that the page was not the next page in thesequence, wherein the program would flow from the decision block 246along the "N" path to the input of function block 252.

Referring now to FIG. 13, there is illustrated a flowchart depicting theoperation of the print module. The program is initiated at a block 260and then proceeds to a decision block 262 to determine if the objectrepresentation of the image has been received. If not, the program flowsalong an "N" path back to the input of decision block 262. When receivedat the PEM, the program will flow from decision block 262 along the "Y"path to a function block 264 to convert the object representation to apixel representation. This is achieved in the RIP 147 associated withthat PEM. The image is then buffered, as indicated by a function block266 and then the program flows to a decision block 268. The decisionblock 268 determines whether the printer is operating with a mechanicalprint buffer. In certain situations, the use of a mechanical printbuffer may significantly increase the cost. In this situation, the pagecan merely be maintained in the image buffer 149 preceding the markingengine 151 until it is necessary to print that document. By knowing thespeed of the print engine, it is then possible to calculate the timefrom initiation of the print operation in the print engine to thecompletion thereof and subsequent ejection of the paper therefrom. Inthis manner, it would not be necessary to buffer the pages in an outputmechanical print buffer.

If the mechanical print buffer is present, the program will flow alongthe "Y" path from the decision block 268 to a function block 272 toprint the page. However, if a recurrent mechanical print buffer was notbeing utilized, the program would flow from the decision block 268 alongthe "N" path to a decision block 270 to determine if the page processcommand had been received from the PMS control task block 120. If not,the program would flow along the "N" path to a decision block 274 todetermine if a timeout had occurred. If not, the program would flowalong an "N" path to a function block 276 to increment the time counterfor the timeout function and then back to the input of decision block270. The system continues in this loop until the timeout counter hadincremented to a maximum value, at which time the program would flowfrom the decision block 274 along the "Y" path to a return block 278.

Once the page process command has been received, the program proceedsalong the "Y" path to the Print Page function block 272 to proceed withthe operation. As described above, proceeding along the path includingthe decision block 270 indicates that there is no mechanical printbuffer disposed on the output of the system. Therefore, when the page isprinted, it will be ejected into the final output paper path; thus, thecontrol system must determine when the page process command istransmitted, which is a function of the processing operations of thePEMs and the time required for this particular page to be processed bythis particular PEM.

After a program has proceeded to the Print Page block 272, the markingengine 151 proceeds to process the image and print it onto the imagecarrier, i.e., the paper. The program then proceeds to a decision block280 in order to determine if a page eject signal has been generated. Ifnot, the program proceeds along an "N" path to a decision block 282 todetermine if a timeout counter has reached maximum. If not, the programflows to a function block 284 to increment the timeout counter and thenback to the input of decision block 280. When the timeout counter hasreached maximum value, the program flows along a "Y" path from thedecision block 282 to a function block 286 to transmit a JAM signal backto the PMS Task Manager 120 to the return block 278. However, if a pageeject signal has been received by the PEM, the program proceeds alongthe "Y" path from the decision block 280 to a function block 288 inorder to send a Page Complete signal back to the PMS task manager 120,and then to a return block 278.

In summary, there has been provided a multiple print engine system whichutilizes a plurality of print engine modules, each print engine moduleconstituting a complete print engine which is operable to receive animage file or an object file, select an image carrier such as paper froma dedicated paper bin and create and print an image onto the paper. Thepaper is then disposed in a print buffer associated with that printengine module. An output combiner or collator is then controlled toselectively assemble the products in the print buffer. An imagedistributor is operable to determine which of the print engine modulesis to receive which of the pages to be printed. By processing the imagesin parallel, each of the print engine modules can utilize a higherquality slower speed engine with the overall print speed beingequivalent to that of a very high speed print engine.

Although the preferred embodiment has been described in detail, itshould be understood that various changes, substitutions and alterationscan be made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A multiple print engine, comprising:a pluralityof electrophotographic print engine modules, each of said print enginemodules operable to receive an image file corresponding to an inputsheet image and for printing the input sheet image on an image carrierfor output therefrom; a plurality of print buffers, each associated withthe output of at least one of said print engine modules, and each ofsaid print buffers operable to receive the output of the associated oneof said print engine modules as a completed print job; and an outputcollator for selectively retrieving the output of each of said pluralityof print buffers in accordance with a predetermined output sequence. 2.The multiple print engine of claim 1, wherein said output collator isoperable to route the output of each of said plurality of print buffersafter retrieval thereof to a single output.
 3. The multiple print engineof claim 1, and further comprising an image distributer for receiving aplurality of the input sheet images and dividing each of the input sheetimages into an image file compatible with each of said print enginemodules and routing the image files to select ones of said print enginemodules in a predetermined input sequence.
 4. The multiple print engineof claim 3, and further comprising a print manager for determining thepredetermined output sequence in which said output collator selectivelyretrieves the output of each of said plurality of said print buffers. 5.The multiple print engine of claim 4, wherein the predetermined sequenceof said output collator comprises the input sequence in which the inputsheet images were input to said image distributor.
 6. The multiple printengine of claim 3, and further comprising a prim completion indicatorfor indicating when one of said print engine modules has completed aprint job and is ready to receive another of the image files from saidimage distributor.
 7. The multiple print engine of claim 6, and furthercomprising a failure indicator for indicating when one of said printengine modules does not complete a print job.
 8. The multiple primengine of claim 7, and further comprising an image buffer for bufferingthe image files such that when said failure indicator indicates that oneof said print engine modules does not complete a print job, anassociated one of the image files can be forwarded to another one ofsaid print engine modules for processing of the associated one of theimage files.
 9. The multiple print engine of claim 3, and furthercomprising a print manager for determining the predetermined outputsequence in which said output collator selectively retrieves the outputof each of said plurality of said print buffers.
 10. The multiple printengine of claim 1, wherein the image carrier comprises paper.
 11. Themultiple print engine of claim 1, wherein only one of said print buffersis associated with each of said print engine modules.
 12. The multipleprint engine of claim 1, wherein each of said print engine modulesoperates at a first speed and said output collator operates at a secondand faster speed than said first speed.
 13. The multiple print engine ofclaim 1, wherein at least one of said print engine modules comprises amulti-pass print engine module operable to create multiple-pass imageson said image carrier.
 14. A multiple print engine, comprising:aplurality of electrophotographic print engine modules, each of saidprint engine modules operable to receive an image file corresponding toan input sheet image and for printing the input sheet image on an imagecarrier for output thereof; a plurality of input image buffers, eachassociated with an image input of at least one of said print enginemodules, each of said image buffers operable in response to a pageprocess command to transfer the stored image file therein to said imageinput of said associated print engine modules for processing thereof toprovide on an output of said associated print engine module a completedprint job; a control system for generating the image files anddistributing the generated image files to select ones of said imagebuffers on select ones of said print engine modules, said control systemoperable to generate and transfer to each of said print engine modules apage process command in a predetermined order.
 15. The multiple printengine of claim 14, and further comprising a print completion indicatorfor indicating one of said print engine modules has completed a printjob and is ready to receive another one of the image files.
 16. Themultiple print engine of claim 15, and further comprising a failureindicator for indicating when one of said print engine modules does notcomplete a print job.
 17. The multiple print engine of claim 14, whereinsaid image carrier comprises paper.
 18. The multiple print engine ofclaim 14, wherein only one of said input image buffers is associatedwith each of the said print engine modules.
 19. The multiple printengine of claim 14, wherein each of said print engine modules isoperable to operate at different speeds.
 20. The multiple print engineof claim 14, wherein at least one of said print engine modules comprisesa multi-pass print engine module operable to create multiple-pass imageson said image carrier.
 21. A method for processing images in a parallelmanner, comprising the steps of:distributing a plurality of image files,each corresponding to an input sheet image, to select ones of aplurality of electrophotographic print engine modules; receiving at theselect ones of the print engine modules the distributed image files,which distributed image files correspond to the input sheet images;printing the sheet images corresponding to the received image files onimage carriers with each of the print engine modules and outputting theimage carriers with the printed sheet images thereon from the associatedones of the print engine modules; buffering the output image carriersfrom each of the print engine modules in one of a plurality of printbuffers that is associated with the associated outputting one of theprint engine modules; and selectively retrieving the output of each ofthe plurality of buffers in accordance with a predetermined outputsequence.
 22. The method of claim 21, wherein the step of selectivelyretrieving the output of each of the plurality of print bufferscomprises routing the output of each of the plurality of print buffersafter retrieval thereof to a single output.
 23. The method of claim 21,and further comprising the steps of:receiving a plurality of the inputsheet images; converting each of the input sheet images into anassociated image file compatible with each of the print engine modules;and routing the image files to the select ones of the print enginemodules in accordance with the step of distributing.
 24. The method ofclaim 23, and further comprising the step of determining thepredetermined output sequence by which the step of selectivelyretrieving the output of each of a plurality of print buffers operates.25. The method of claim 24, wherein the step of distributing operates inaccordance with a predetermined input sequence of receiving.
 26. Themethod of claim 23, and further comprising, indicating when one of theprint engine modules has completed a print job and is ready to receiveanother one of the image files, wherein the step of distributing isoperable to distribute the other one of the image files to the printengine module.
 27. The method of claim 26, and further comprisingindicating when one of the print engine modules does not complete aprint job.
 28. The method of claim 27, and further comprising bufferingthe image files in an image buffer such that when the step of indicatingindicates that when one of the print engine modules has not completed aprint job, the associated one of the image files can be forwarded toanother one of the print engine modules for processing of the associatedone of the image files as an image.
 29. The method of claim 23, andfurther comprising the step of determining the predetermined outputsequence.
 30. The method of claim 21, wherein the step of printing thesheet images onto the image carriers comprises processing the imagefiles to print an associated one of the sheet images onto paper.
 31. Themethod of claim 21, wherein the step of printing with the print enginemodules is operable to process at a first speed, and the step ofselectively retrieving operates at a faster speed than said first speed.32. The method of claim 21, wherein the step of printing with each ofthe print engine modules comprises printing one of the sheet imagesassociated with an associated one of the image files with at least oneof the print engine modules to perform a multi-pass print operation tocreate multiple-pass images on a respective one of the image carriers.